Flowmeters that measure fluid in a gaseous state, such as oxygen, nitrogen or nitric oxide, are often used to dispense the fluid in prescribed doses for therapeutic purposes. As an example, patients requiring oxygen obtain a prescription for a certain concentration of oxygen, a certain flowrate or volume of oxygen, and a certain time period for the delivery of oxygen. The oxygen is delivered from an oxygen source, such as an oxygen concentrator, through the flowmeter, to the patient. When the oxygen is delivered from the oxygen source, it is measured by the flowmeter and adjusted by the regulator to dispense the appropriate flowrate of oxygen for delivery to the patient.
Known flowmeters are generally in fluid communication with an oxygen source and have a ball indicator for indicating the flow rate to the user. Such flowmeters may include a meter body having an inlet port, and an outlet port. Downstream of the inlet port and upstream of the outlet port is a “Thorpe” tube that houses the ball indicator. Oxygen flows into the meter body at the inlet port, through the Thorpe tube, and out the outlet port. The oxygen in the Thorpe tube elevates a ball of the ball indicator upwards against gravity. A visual comparison of the ball up with an adjacent flowtube scale within the Thorpe tube indicates the flow rate of oxygen through the flowmeter. A regulator is adjustable by the user, and is operated by a knob to alter the flow through a fluid communication channel in the flowmeter. The regulator may be a needle valve, including a needle portion that extends into the fluid communication channel adjacent the outlet. Typically, the valve shaft is threaded, and receives an internally threaded boss. By rotating an associated knob, the needle moves axially to either be inserted into, or pulled away from, the fluid communication channel, which operates to open or close the outlet. When the user adjusts the knob, the flowrate through the fluid communication channel is changed. Corresponding flowrate information is obtained by a visual inspection of the suspended ball aligned against the flowtube scale.
There are several drawbacks of flowmeters of the above description. In one example, there can be difficultly in a user to comparing the alignment of the ball against the scale. Further, when flowrate falls outside of prescribed ranges, it is incumbent on the user to visually inspect the location of the ball on the scale, to acknowledge that the ball is out of range, and to adjust the knob of the regulator until the condition is back within the prescribed range.